Month: July 2015

I recently carried out a substantial investigation into a relatively new build property in County Durham. The property was 6 years old and still covered by the NHBC Buildmark warranty. The property was suffering from major problems with damp and as always I warned the client of the need for invasive survey work.

I can’t cover all the defects found in a short blog but the flooring defects found are interesting because the construction methods used are rather odd.

Essentially the property was suffering quite seriously from wall base damp. The walls were dry lined on dot and dabs and in places the plasterboard was so damp it was crumbling. The client had an expensive hardwood floor down and this was ruined with damp staining and swelling of the timber.

Ruined Hardwood Flooring

The only way to fully understand what was going on was to take up flooring and expose the substrate. Skirting boards were removed and the hardwood flooring came up. We found the floor to be laid on a standard chipboard oversite and I’m sure you know what happens to chipboard when it gets wet, particularly when it is not bathroom grade. The chipboard was also taken up and we found that the solid floor was covered with Kingspan insulation slabs, these too were saturated and we removed a section of insulation to see what was under this. Incredibly, what we eventually found was that there appeared to no concrete floor screed installed. The SAM was supposed to be laid on a 75mm reinforced sand and cement screed but all we found was a compacted hardcore base covered with a thick layer of black Visqueen SAM (self adhesive membrane) acting as a DPM.

There were numerous serious faults with the installation of the Visqueen SAM even had it been laid correctly on a 75mm screed…

The membrane had not been overlapped anywhere near the required 150mm and in fact had already failed at joints. One failure was apparent enough for us to be able to use deep wall probes through the gap in the membrane to check whether the underlying masonry was damp. See next image.

Deep wall probes indicate that the underlying wall is saturated

The overlap on the membrane was around 10mm rather than the required 150mm.

On removing a large section of chipboard and Kingspan insulation from the floor we immediately noted that the Visqueen SAM was severely punctured due to underlying sharp objects. See image.

Badly punctured Visqueen SAM

3. The Visqueen SAM was not installed to manufacturers requirements nor did it meet the installation standards required to maintain its BBA accreditation.

4. The Visqueen was simply turned up the concrete block wall and was not connected to a physical damp proof course in the wall because there was no physical damp proof course installed in the wall. This resulted in severe saturation of the concrete wall base with 6.5% total moisture content recorded above the level of the SAM membrane. See image.

No DPC to party wall and saturated wall base

The choice of Visqueen SAM as a physical DPM was utterly bizarre for what should have been a straight forward 1200 gauge DPM sheet installation but we can only assume that due to the thickness of the material the rogue builder thought he’d get away with not installing the floor screed. He was of course wrong and the SAM was badly punctured by the underlying aggregate in numerous locations. Defects in this property ran to a 28 page report excluding any appendix material and whilst I wish I was surprised to find work of this quality, sadly it is all too frequent.

A regular client with a portfolio of properties recently sent me some images of a particular damp problem to the rear kitchen extension of the property they had recently let. They knew there was some minor dampness to the head of the kitchen wall but expected that this was a result of the property standing vacant for a long time and they thought it would dry once occupied. To my mind there is no good reason for vacant properties to be damp but in any event on seeing the images it was fairly obvious that the property had a severe penetrating damp problem to the head of the rear kitchen wall.

Penetrating damp above kitchen window

They appointed me to investigate the problem and when I arrived I noted that it was a single storey extension with a parapet wall directly above the damp kitchen wall. It has got to the point that if I see a parapet wall I know it has defects and has been detailed incorrectly so I always open up to confirm.Out came the telescopic ladders and I accessed the flat roof deck to be met with the following site.

Narrow coping stones to parapet head

It was immediately obvious that the coping stones were too narrow for the application but I also noted that the mortar joints were heavily eroded and seemed to be comprised almost entirely of red sand. I scraped the joint and it was clear that the sand had only been mildly threatened with the possibility of any cement.

What, no cement?

I lifted off a coping stone and as expected saw that critical technical details were absent. The was no hard support across the cavity and no physical damp proof course installed. The parapets would continue to take in rainwater until these defects were corrected.

No physical DPC or hard support installed

There are a number of proprietary systems on the market now for securing copings, such as cavity lock systems, and there are even proprietary hard supports available to bridge the head of the cavity but in the absence of any of those systems I have detailed the method that can easily be achieved by any reasonably skilled builder with readily available tools and materials.

I always include a drawing of the correct technical detail in my reports so that this can be given to the contractor because it is rare to find builders who understand the required technical detailing, which is odd because parapet walls are becoming a very common feature on some new build sites. If you’re interested in that detail then here it is…

I am currently engaged on a construction dispute in which the cost of building an extension somehow escalated to around £60k over and above the original £70k quote from the builder. I was initially called in to inspect and assess building defects relating to the works and the client was quite staggered at the range and number of defects found and I simply could not see where the additional £60k had been spent.

The builder had claimed an additional sum of money for ‘roof strengthening works’ and anecdotally I am informed that the client received a call from the builder when discovering that the roof rafters were structurally unsound and indeed, they were. At some point in the buildings history, changes had been made to the roof pitch and/or height and new rafters of the correct length and cross section should really have been installed to stretch from ridge board to wall plate. However, the builder at that time simply decided to nail extra lengths of timber onto the rafters and the roof was completed in the manner you see in this image.

Historic alterations to the buildings roof left the roof structure in this condition.

So, our builder, bless his cotton socks, was absolutely right; the roof structure was unsound and required strengthening, something that he could deal with at additional ‘reasonable’ cost.

Sadly however, what the builder actually did was make the same mistake again and simply nailed on even more bits of wood so we ended up with a three leaf rafter sandwich. Rafters were not properly coach bolted together and neither were the repair sections long enough to reach the wall plate. In fact, even the sections were undersized and the builder dealt with this by packing between the purlin and the repair sections with bits of cut plywood.

Three ply rafter sandwich but not much meat.

These were fairly major roofing work to a portion of the building and what is worse is that the builder only saw fit to report on the sections of the roof affected by his work to the new extension.

The main roof of the building was also structurally unsound and whilst this had nothing to do with the current builder, surely a responsible builder would have reported this to the client and given them an opportunity to deal with the whole roof structure whilst works were ongoing.

New ‘strengthening’ rafters cut short and packed with plywood

I do know that the client would have taken the opportunity to deal with these structural defects in the whole roof but as it happens they also have to deal with the part of the roof that was allegedly strengthened . Needless to say, the cost of ‘roof strengthening’ works forms part of a rather large defect and cost schedule that is currently in the hands of my clients construction lawyer.

Failure Modes in Blown Fibre Insulation

I suspect that the day of reckoning is fast approaching for irresponsible Cavity Wall Insulation installers but to date the campaign and public outcry against CWI failures has primarily centered on poor specification and installation. However, I think there is another very important question that should be asked… for those properties that were subject to a reasonable level of due diligence, responsible pre-survey work and sound installation methods, is it possible that even those installations may have failed despite all the installers best efforts? Sadly, the answer is a resounding yes and it’s an answer I give based on pragmatic experience on what I’ve been finding on site for a number of years.

I have been warning my clients against using blown fibre cavity wall insulation for quite some time because as part of the damp investigation process I frequently open up cavities or at least inspect them with a borescope. I firmly believe that blown fibre cavity wall fill is responsible for the vast majority of failures relating to CWI installation and I generally discuss two modes of failure in my reports.

Dry Slump: Dry slump occurs within a very short period of having the blown fibre installed and how much it slumps depends on how well it is installed. A loose fill will slump significantly more than a tightly packed fill and you would be amazed at just how quickly this slumping can occur. I have rechecked properties within a week of first inspecting them with a thermal imaging camera and found that the walls now contain zero fill within the top 12 inches of the wall. Where a previous problem existed with cold surface condensation, then homeowners find that the problem revisits them but with a focus on the top sections of the internal walls that no longer benefit from CWI due to its slumping effect.

Realistically, all properties would be best having a follow up visit to top up the fibre CWI after it has slumped but this rarely, if ever occurs.

Wet Slump: To my mind, this is the biggest problem with blown fibre CWI because when this mode of failure occurs it creates a problem above and beyond the obvious lack of thermal improvement to the building fabric. Blown fibre CWI, unlike blown polystyrene beads, is not inherently waterproof and I consistently find it completely slumped to the bottom of the cavity in a wet mushy mess. If you imagine holding up a bed quilt filled with blown fibre, holding it by two corners. You’ll probably find that the fibre is evenly distributed throughout the quilt. Now if you were to get an assistant to saturate the quilt with a hose-pipe you would quickly find that the saturated blown fibre slumps to the bottom of the duvet case in a wet soggy mess. This is essentially exactly what happens within the cavity wall, particularly for those properties that have an issue with penetrating damp to the outer leaf of brickwork. The resultant technical problem is that you will potentially have a very serious wall base damp problem caused by bridging of the cavity wall and physical damp proof course and of course no benefit whatsoever from the alleged improvement in insulation.

Dry and Wet Slump to Blown Fibre CWI

Aside from wet or dry slump, I consistently see the problem of inconsistent and patchy fill. This problem is fairly obvious under thermal imaging and it is more unusual to find solid and consistent levels of fill than it is to find empty voids in the cavity. I think this problem has been fairly well reported and I’ve seen a number of thermal images online aside from my own that highlight the problem.

I notice that the ‘all damp is caused by cavity wall insulation’ party are using this piece to promote their cause and whilst I have no objection to that it should be read in conjunction with this piece to bring a sense of balance to the discussion… Is all cavity wall insulation bad?

More new build woes unfortunately, this time relating to poor installation of extraction systems. Multivent installations are becoming increasingly popular in new build properties due to concerns relating to air tightness; they are an improvement on single room extraction fans and significantly cheaper to install than whole house MVHR systems.

This particular fan was continuous running and designed to be ultra quiet which is great because I generally find that fans get turned off wherever the noise levels are intrusive. I’ve been recommending and specifying continuous silent running centrifugal fans for quite a few years now.

Unfortunately there was clearly something wrong because I checked the ceiling mushroom outlets and they were not drawing any air whatsoever. I asked the client about this and they explained that they had turned the extract fan off about a week previously after noise levels were so high that it kept them up all night. In fact after a sleepless night the frustrated home owner went into the loft space in the very early hours of the morning and adjusted the motor speed control to its lowest setting to stop the noise. They complained about this to the developer the next day who claimed that not all their properties had fans installed but because they lived so close to the train tracks it had been installed especially to help deal with the noisy trains. I pointed out to my client that the developer was required to install an extraction system in all properties under the approved documents and the fan should be quiet.

A closer inspection of the installation was warranted because I know these systems are generally very quiet when correctly installed. On accessing the loft space I found that the developer had laid an old piece of wood across the bottom chords of the trussed rafter and simply sat the extraction unit on top of the loose piece of wood.

Poorly installed multi vent fan

They can be mounted horizontally or vertically but in this case the extraction unit should have been fixed to a secure plinth with the special installation screws that come supplied with the unit. Motors are finely balanced in these units but they will move around under the centrifugal forces generated if not properly secured. Moreover the isolation screw installation is critical to prevent sound transmission through the building.

The other thing I really do not like to see is ducting secured with cable ties and in this case there was already a section of ducting disconnected due to this poor fixing method. The consequences of having an extractor fan pumping moist air into the loft space could have an extremely deleterious effect on the roof timbers and consequently end up being an extremely expensive latent defect for the developer.

I was carrying out a dilapidation survey in the West Midlands quite recently and whilst checking the roof space came across an unusual case of roof spread. I’m sure you’re familiar with the basic cause of roof spread but if you aren’t then I’ve included a basic diagram that shows how unrestrained rafters can apply horizontal thrust to the walls and make them unstable. Generally this is due to inadequate collar ties or ceiling joists or indeed failure of those timbers. In this particular case there were no external signs of cracking or structural problems and neither was I particularly looking for, or asked to investigate structural cracking in the building. However, on inspecting the first floor store room I noticed substantial cracking to the dividing party wall that warranted more detailed investigation.

There was a long crack to the internal corner of the ceiling to wall junction on the front elevation of the property and a further diagonal crack cutting down through the dividing party wall.

The damage was indicative of roof spread but was not quite serious enough to manifest any obvious visual problems to the front elevation of the property.

The roof space to this particular property was not fully accessible or safe to access so I had to inspect as best as I could from the loft hatch and after a couple of minutes I looked directly above my head and immediately noticed the problem. The ridge board was completely split which had resulted in a section of the rafters dropping just enough to apply horizontal thrust to the wall plate on the front elevation. If looking for the obvious and common cause of roof spread then this particular issue could so easily have been missed, especially when limited to a head and shoulders inspection from the loft hatch.

I have previously written about the risks of installing External Wall Insulation without due consideration to the building, the system design and adequate site storage facilities and site management. The article, titled, ‘The Risky Business of Covering Up’ was published in the CIOB’s Construction, Research and Innovation Journal can be found here under the heading ‘published material’…

I have been predicting that we would see a glut of external wall insulation failures for the last three years and I am now seeing strong signs that my prediction is correct and I suspect that even I have not fully grasped the scale of the problem yet. I am currently working on a supplementary article to follow the piece I wrote in the CRI Journal and to that end have a trip to Germany planned to review their EWI system failures.

To my mind the industry is simply not open enough to airing and discussing their failures and in fact has a very strong defence mechanism that kicks in to counter negative web publicity wherever it appears. I have experienced this first hand when I recently blogged that ‘The Defects are Often Built In.’ I was following and photographing a Midlands EWI High-Rise installation purely as an academic piece and was careful to not mention the contractor or the particular scheme. Apparently I was not careful enough because within 24 Hours I received a call from a manager who project manages these schemes for the contractor concerned. He explained that he had received a call from a ‘concerned industry insider’ and that he wanted to discuss my blog. In fact he was incredibly reasonable about the blog and was more concerned about the quality of work seen in my blog pictures. One picture was flagged with a large number of defects and he was in complete agreement that the work was appalling. His prime concern was being proactive in getting the work rectified before premature failure placed his employer at considerable financial risk. We had a very professional discussion and I closed by commending his approach wishing him good luck in getting the work rectified. Twenty four hours later I received a second phone call from the Managing Director directly responsible for the site and the work. His approach was very different, he claimed that the photograph was only good for the time it was taken and that I didn’t know what had happened afterwards. His ‘experts’ were telling him that the work was good and there was a reason that mechanical fixings were not fully installed at the same time. I disagreed and stated that the installation process was clearly detailed in the BBA certificate. He suggested that they had an installation process that had been signed off by their designer but of course if this deviated from the BBA certification process then the BBA certification process would no longer be valid. In essence he claimed that there was a reason that only one mechanical fixing was being installed into a 1200 x 600 insulation panel until the adhesive had dried, after which point they would go back and install the extra fixings required. This was patent nonsense because their approach to installing insulation panels was inconsistent on every high rise block and every elevation of each high rise block. Some panels had zero fixings, some had one, some had two some had three…. You get the picture. If there was a separate site installation process deviating from the BBA certificated process then this in itself is a problem but clearly there can only be one process and inconsistency of approach demonstrates clearly that the process is not being followed or managed. There was a subtle suggestion that coming to site to discuss how things are done might present some ‘opportunities’ for my business whilst continuing to run with my damaging blog might be damaging to my business. I try to be pragmatic wherever possible and compromised on removing the name of the town, changing the photograph to one more palatable and removing the project value so the blog was as anonymous as it could possibly be. I refused the suggestion that I should take down the blog altogether.

What really fascinated me about this conversation is how quickly the EWI industry defence mechanism kicked in. I was told that the web is scanned daily for negative publicity and a concerned party from within the EWI trade association contacted the contractor within 24 hours of my blog going live. I was told that there is a possibility that my blog or website was possibly being specifically monitored due to my previous article on EWI system failures. I’m well aware that this sounds like some fantastic conspiracy theory but its rather more simple than that… EWI is big business and confidence in EWI system installations has to be maintained to keep the gravy train on track. Perhaps the great irony in all this is that I am a huge fan of EWI systems but my view is that they are consistently let down by inadequate design and poor site practice and installation and some reform is needed.

What I don’t want to do is get into criticizing individual contractors but I am seeing more EWI insulation work done poorly than done well and I hold a view that inadequate design and poor site quality control are often the primary causes of failure. My research and writing on EWI failures is purely academic and aimed and at raising awareness with clients of the need to stringently manage site works. Secondly, clients need to understand their ongoing maintenance obligations with regard to protecting the long term guarantees on these systems. A client may have a £1m EWI system installed to a high rise block that he believes is guaranteed for thirty years but if they do not have a regular maintenance regime in place to inspect building joints, particularly around window and door frames, then they will hand their EWI system guarantor a rather large get out clause should the system fail prematurely. In my experience a very small minority of clients set up planned maintenance regimes once these systems are installed and yet the requirement to set up a regular inspection and maintenance regime should be clearly presented to the client at project handover. I have managed millions of pounds worth of EWI installs and not once was this requirement set out or explained to the client. The failure to set up a regular maintenance regime may well prove to be a great get out clause in some isolated cases but my experience is that, more often than not, the defects are built in and as my construction solicitor recently commented, ‘You cannot maintain a defect.’

The Department of Energy and Climate Change insisted that EWI systems came with a 25 year guarantee to facilitate rolling out EWI systems to the mass market and to that end SWIGA provide a guarantee that covers materials and workmanship.

The problem with SWIGA is twofold:

Firstly, SWIGA was essentially set up by the EWI industry and it is not what I would call an independent body. Secondly, if a client does experience EWI system failure that is reported to SWIGA then SWIGA will appoint the system designer or manufacturer to investigate that failure. This is hardly an independent investigation and one that is bound to develop into a circular argument as installers then appoint their own experts to counter the findings in reports generated by designers or manufacturers. I’ve seen this first hand on numerous occasions now and can see an EWI industry heading towards a tangle on internal conflict and dispute until they accept that they cannot self-regulate to the degree that they currently are.

EWI systems will continue to be a potentially great way of dealing with technically obsolete and ‘hard to treat’ properties but the industry is in danger of leaving a legacy of system failures and a subsequent tarnish that will be very difficult to remove unless wholesale changes are made. I would suggest that adequate reform rather than the management of negative publicity is the way to maintain consumer confidence in EWI system installations.

This article on rising damp was first published on ‘surveyingproperty.blogspot’ and later reproduced in a SAVA technical bulletin, (issue 17, 2014). Since it is my own material then I thought it was long overdue for inclusion on my own blog site. I have further supplemented and updated the information by the inclusion of a damp investigation flowchart that I developed for inclusion in a book I am writing. Please note that this flowchart is the copywrite material of the author and should not be reprinted or posted elsewhere without the authors permission.

Deep wall probes in use

My own level of expertise regarding rising damp stems from two years research carried out into rising damp that resulted in a dissertation entitled, “The Efficacy of DPC Injection”. I have been actively involved in surveying damp properties and more importantly, teaching damp investigation for a number of years now and think there have been a number of significant developments over the last ten years to merit an update on current thinking, controversies and industry developments.

There have been a number of commentators who have done nothing to move this issue forward over the last few years. In particular Jeff Howell’s book, “The Rising Damp Myth”. Stephen Boniface, former Chair of the RICS Building Surveying Faculty, has also gone on record to state his belief that rising damp is a myth.

NB.It is worth noting that since this article was first published, Stephen Boniface has gone on record in stating that he has was misquoted on this issue.

Whilst I understand the sentiment behind their extreme view, it is perhaps a backlash to a DPC industry that promotes rising damp as a common occurrence.

During my research into rising damp, I came across a PCA examination paper for their National Certificate in Remedial Treatment from 2005 where a question started with the statement that, “Rising damp is a common problem”. Of course we know it is not a common problem but it demonstrates the second of two extremes when a rather more moderate approach needs adopting. Both views cause a number of problems:

 The view that rising damp is a myth may cause building surveyors to form a view that it is not worth learning how to properly survey for rising damp.

 The supposition that rising damp is a common problem has led to a glut of poorly trained industry surveyors and widespread misdiagnosis due to over reliance on hand held electrical moisture meters.

Even the poorly trained have a real sense of security gained in the knowledge that, even if you misdiagnose, the waterproof renovating plasters applied internally will give the appearance of a dry wall, thereby leading clients to conclude that your diagnosis was correct. After carrying out a substantial literature review on this question I can with confidence state two facts:

1. Rising damp does exist and is a scientifically proven phenomenon.

2. Although it exists, it is incredibly rare.

The more common academic view is that between 5% and 10% of damp properties will be affected by rising damp; my own research puts the incidence at less than 5%. (Note that we are talking about a percentage of damp properties here and not total properties in the UK.)

So what exactly is rising damp?

The simple academic description would describe rising damp as “an upward capillary migration of water in masonry”. You will find the reference to capillary action in most text books and it is in this area that most text books are long overdue an update. Bricks contain capillaries or microscopic tubes that are small enough to allow inter-molecular attractive forces between the liquid and solid surrounding surface; these forces allow a liquid to flow in narrow spaces against gravity. The problem here is that we now know that rising damp has two moisture transfer mechanisms, i.e. capillary action and diffusion.

It is generally thought that molecular diffusion (Fickian) is the moisture transport mechanism for water molecules moving through cement paste. Some of you may remember this from your school physics lessons but in simple terms diffusion is the spreading of solutes from regions of highest to regions of lower concentrations caused by the concentration gradient. It is the same for concrete floor slabs; water moves up through the floor slab by a process of diffusion and not capillary action.

A new definition for rising damp

It is time to propose a new definition for rising damp and I would suggest the following description:

“Rising damp is an upward migration of groundwater in masonry walls. It will act in combination on the masonry units and their separating mortar joints or it will act primarily on the mortar joints. The moisture transfer mechanism in masonry is capillary action whilst the moisture transfer mechanism within mortar is diffusion. The major moisture pathway for rising damp is the mortar perps so it can be stated that there are dual moisture transfer mechanisms for rising damp, diffusion and capillary action.”

Maybe not as snappy as the original definition but it clears up a number of issues and in itself can be used as an aid to diagnosis and specification.

Since we know that the mortar joints are primarily affected then it serves very little purpose in drilling and injecting brickwork without also treating the mortar joints. We need to qualify this statement because we have something of an anomaly when it comes to discussing the mortar joints.

Tests were carried out at South Bank University a number of years back which failed to replicate rising damp in laboratory conditions. The tests were bound to fail because account was not taken for the fact that a new DPC mortar bed is impermeable to moisture. However, after 30-50 years of environmental exposure the mortar degrades and rather than providing an impermeable barrier, it then becomes the main moisture pathway.

For reasons of practicality and aesthetics we should have completely moved away from injecting brickwork and retrofit DPC injection should focus on the mortar bed and perp joints. However, we are getting ahead of ourselves because we’ve not yet discussed correct diagnosis.

It makes no sense whatsoever to install a retrofit chemical injection to a property that already has a physical DPC installed unless you can evidence failure of the existing DPC; to my knowledge, no one has yet done this.

Diagnosing rising damp

There is a view within the damp proofing industry that rising damp can be diagnosed with nothing more than a hand held electrical conductance meter and a great deal of experience. There is not a shred of scientific evidence to support this view and in fact it is well documented that hand held electrical moisture meters are of limited use due to the fact that they are calibrated for timber and not masonry. They are also prone to giving false positive readings for damp wherever they encounter salts, carbonaceous materials or backing papers such as foil damp.

You need to confirm that three conditions are present to definitively confirm a case of rising damp:

1. You must have a rising damp moisture profile. That is a profile that is wetter at the wall base but gradually decreases with height to a theoretical maximum height of circa 1.5 m.

2. You must prove that moisture is present at depth in the masonry and it is not enough to take surface readings from the plasterwork. You will need deep wall probes or a calcium carbide (speedy) meter to confirm this on site.

3. You will need to confirm that nitrates are present in the damp apex of your moisture profile. This will involve doing on-site analysis or sending a sample off to the labs. You might have noted that I have ignored chloride salts because these can be present in tap water or building materials. A positive test for nitrates confirms that the moisture has leached up from the soil.

NB. I have since discussed and debunked the academic requirement for salts analysis in a later article entitled, ‘Rising Damp: An update for 2015.’

Unless you can confirm each of these three conditions then, your diagnosis is based on guesswork. On the upside, due to the use of waterproof renovating plasters no one will ever know you got it wrong. It is a fact that the application of renovating plaster provides the perfect cover up for bad surveying practice.

The following flowchart illustrates the damp investigation process that we teach on our damp investigation training course.

Damp Investigation Process Flowchart

Do physical DPCs fail?

This was a key question asked in my research and I could not find a shred of evidence to support the view that physical DPCs fail though I accept that not enough research has been done in this area.

I did note that cracked slate DPCs had been found but as one of my contemporaries wisely pointed out: “A crack is a crack and a capillary is a capillary”, you will hopefully see the logic in this statement.

Slate DPC still fully functional in a building that is circa 140 years old.

What is clear is that DPCs are regularly found to be bridged or compromised in some other way.

How has the damp proofing industry changed in the last ten years? It is fair to say that the process of retrofit DPC injection has been taken out of specialist hands over the last ten years. In the past, expensive equipment and specialist training was required for injecting siliconate and stearate fluids into brickwork. These are still used, but the market has moved more towards the use of aqueous silane creams injected into mortar bed and perp joints.

The process is so simple that anyone with a reasonable degree of DIY skill can successfully carry out chemical injection. All that is needed is a hammer drill, a tube of your chosen water repellant cream and an application gun.

The cream is applied into 12 mm holes drilled at 120 mm intervals which will then diffuse into the wall via the mortar course to form a damp course to BS 6576. The drillings are simply made good with re-pointing rather than being sealed with plastic plugs, as used to be the case. Moreover, aqueous silane creams are far safer to use than the old types of injection fluids and come with far less chance of user error; anyone who ever used these fluids will tell you how they burned in contact with the skin.

It was not unusual for pressure injected fluids to be injected into voids within the brick and in any event these fluids were never designed to give full penetration that forms a continuous barrier to damp.

They worked by a process called viscous fingering which in basic terms means that you have fingers of waterproofing within the individual masonry unit rather than a complete barrier.

The best you could hope for was that you stop a fraction of water rising in the wall and restore moisture equilibrium. Moisture equilibrium is achieved when water is evaporating off the wall as fast as the damp is rising; thereby controlling any further rise in height of the damp. Silane creams are designed to give a complete impervious barrier to damp and on that basis alone outperform the old liquid systems.

Retrofit DPC injection has always been a two part management solution with the internal re-plastering being as, if not more important, than the injection work. Plaster becomes defective when chronic damp dissolves the calcium sulphate within the plaster, which make it extremely porous but salt contamination is the primary reason to hack off and replace the plaster. These salt contaminants are hygroscopic and will continue to absorb moisture from the atmosphere causing the wall to remain damp.

In the early days it was common for plaster to be hacked off and replaced with sand and cement render containing a waterproof additive that was then finished with a coat of Carlite finish. These days waterproof renders are rarely used with most contractors and specifiers opting for one in a range of waterproof renovating plasters that have become available.

For the record, I am neither anti damp proofing industry nor anti retrofit injection; I simply believe that the vast majority of damp buildings can be cured at source using nothing more than minor building works and the damp proofing industry would be best served by accounting for this fact.

I have both specified retrofit DPC injection and used it personally because pragmatically occasions do arise when you can do little else. What if a neighbour’s yard has higher ground levels than yours and is draining against you gable wall? It is unlikely that lowering your neighbour’s ground levels will be an option. A truly independent and competent damp surveyor will not hold with extremist views that rising damp is a myth but will also understand that rising damp is incredibly rare. It is this reasoned and pragmatic approach that will leave them best placed to appropriately specify works to achieve a cure or a management solution. Wherever possible, a cure should always be the preferred option and retrofit DPC injection falls firmly under the heading of management solution.

When carrying out new build inspections you will inevitably venture into areas of subjectivity when it comes to judging whether building aesthetics meet a reasonable standard.

With regard to brickwork it is reasonable to expect that bricks are of a consistent batch, that brickwork is clean and free from major chips or cracks, that bed joints are level and perp joints are plumb. Mortar joints should be evenly spaced, neatly pointed and mortar should have been carefully gauged to ensure a consistent colour match. The physical damp proof course should also be visible where it overlaps the bed joint by around 5-10mm, if it is not then it has not been installed or it has been bridged.

Interestingly masonry walls are generally stronger when built with thin joints and as a general rule of thumb we expect to see mortar joints of around 10mm thickness in the UK and even less for thin joint construction. Overly wide mortar joints are susceptible to cracking and weaken the structure.

The title of this blog came from a conversation I overheard whilst I was inspecting the brickwork on a Bovis site in Long Buckby, Northamptonshire. An employee of this particular large National developer was explaining to the resident how the problem with surveyors like me was that we often had overly high expectations and these expectations needed to be tempered. The brickwork on this particular property was possibly the worst new construction I’ve seen in 20 years and I’d describe the build standard as careless and amateurish, but perhaps my expectations are too high, which is why I’ve posted a series of images detailing what I see as an unacceptable standard of construction. I’d be interested to know if readers of this blog would accept this standard of construction on their new property?

Quality Construction?

I carried out another detailed inspection of a new build property in Northamptonshire today and was immediately alarmed at the poor finishing seen to the stepped lead and apron flashings on the front elevation. Coincidentally, the brickwork was the worst I’ve ever seen on a new build property but that will be the subject of another blog. I am consistently finding that developers do not seem to understand the technical requirements when it comes to installing leadwork and I always advocate the need to investigate the quality of lead installation beyond surface appearances; particularly when surface appearances are as bad as seen in our first image.

Lead should be turned into the bed joint a a minimum of 25mm and should be securely lead pegged at 450mm centres. Once pegged the bed joint can be pointed up or sealed with a proprietary lead sealant. Lead has an incredibly high coefficient of expansion, which is why it should not exceed lengths of 1.5m when installed, this is all about limiting or managing the level of differential expansion at junction details. Failure to allow for differential expansion is a primary cause of lead flashing failure. This particular apron flashing was installed to the garage entrance porch so was accessible for closer inspection from a ladder. Lifting the apron revealed an easy route into the building for wind driven rain and NHBC guidance had not been followed with regard to extending the sarking membrane and turning it up the wall underneath the apron flashings. The NHBC recently released a technical bulletin that included a reference to this common defect, it is one they are consistently finding and my experience of this problem mirrors theirs. So even if the apron flashings were correctly installed there is no secondary barrier to prevent issues with wind driven rain. The keen eyed amongst you may have noticed that a lead securing wedge is visible to the left hand side of the bed joint in the first image. Whilst this inspires some hope that the lead has been securely wedged this hope is offset by virtue of the fact that the wedge is visible. A correctly installed lead peg or wedge should not be visible and if it is then the weather resistance of the bed joint is compromised in that area. When suspicions are raised to the degree they were raised on this inspection then there is a strong argument for gently tugging the corner of the lead. Correctly installed lead will not move whereas poorly installed lead will tend to do this…

Lead not turned into bed joint by the required 25mm

There was 5mm of lead turned into the bed joint as opposed to the required 25mm and lead wedges were installed but not providing a tight interference fit to secure the lead. In fact the only thing holding the 5mm of lead in place was a bead of grey mastic and this lead apron was always destined for very early failure. On the upside, the installer had managed to overlap sections of lead by the minimum required 100mm but there was very little else to redeem this installation.

The lead aprons to the garage porch were further susceptible to wind driven rain because there had been a complete failure to clip the free edge of the lead at 450mm centres; this would prevent wind from lifting the lead and therefore increasing vulnerability to rain.

Leading edge of lead apron not clipped

Moreover, the lead apron flashings were further susceptible to wind driven rain since the roofer had failed to comply with NHBC requirements relating to the need to overlap sarking membrane and turn it up the wall by the minimum required 75mm.

Where is the sarking?

Incidentally, I also measured the lead thickness with a micrometer to ensure that code 4 lead was installed and it was the required 1.8mm; it is not unusual for me to find that cheaper code 3 lead has been installed. It worries me that the plumbers art of installing lead to a high standard is becoming lost but in this particular case the lead installations were as simple as it gets. You can make up your own mind as to whether this is poor quality workmanship, complete ignorance of the guidelines relating to lead flashing installation or a combination of both problems. Joe Malone BSc(Hons) MCIOB MCABE